1. Field of the Invention:
This invention relates to a hose connecting structure obtained by press fitting a hard pipe into a flexible hose, such as of rubber, while expanding the latter radially to a certain extent. This type of structure is often employed for connecting, for example, hoses and a branched hard pipe in an automobile engine compartment.
2. Description of the Related Art:
In an assembly in which a hard pipe is simply press fitted into a flexible hose, the hose is likely to slip off easily. Therefore, various proposals have been made to join a hose to a pipe in such a way that the hose may not easily slip off the pipe. For example, an adhesive is employed for bonding the inner surface of a hose to the outer surface of a pipe. According to another proposal, an O-ring is interposed between a flexible hose and a hard pipe. Still another proposal is shown in FIG. 1, which relies upon a clip 3 fitted about a hose 2 for holding it against a pipe 1 press fitted in the hose 2. These methods are, however, generally not satisfactory in working efficiency, and they do not always make a hose connecting structure which is satisfactory in pull-out strength and sealing properties. Moreover, a lug 4 projecting from the clip 3 is an obstacle in, for example, engine compartments of recent automobiles having a high density of installed items.
An assembly proposed more recently to overcome those problems is obtained by press fitting a hard pipe having stoppers projecting from its outer periphery into a flexible hose. For example, Japanese Patent Application Laid-Open No. 331894/1992 discloses a hard pipe 6 having stoppers 5 formed on its outer periphery by exchange mold injection from a soft material, and pressed fitted in a flexible hose 7, as shown in FIG. 2. Japanese Patent Application Laid-Open No. 159077/1997 discloses a branched pipe 8 of a hard material having three branches 9 each having formed on its outer periphery stop ridges 10 each having a cross section terminating in a sharp edge, each branch 9 being press fitted in a flexible hose 12 having a reinforcing fiber layer 11 in its wall, as shown in FIG. 3.
The methods as disclosed in those two Japanese patent applications are better in working efficiency than the previously known ones as described before, since the connecting work is completed merely by press fitting a pipe into a hose. They are, however, still not always satisfactory in pull-out strength and sealing properties. In Japanese Patent Application Laid-Open No. 331894/1992, the stoppers 5 as shown in FIG. 2 are formed separately from the pipe 6, and even if the advantages of their exchange mold injection may be taken into account, a strong pull-out force acting upon the assembly is likely to cause the stoppers 5 to come off the pipe 6 or become displaced and thus it is feared that the assembly will not maintain satisfactory pull-out strength and sealing properties. In Japanese Patent Application Laid-Open No. 159077/1997, the ridges 10 as shown in FIG. 3 form integral parts of the pipe, but their hard and sharp edges are held against the inner surfaces of the hoses 12 so tightly that if there is a strong impact upon the assembly, the hoses 12 may be damaged by the edges of the ridges 10 and lose sealing properties. As each hose is expanded to a greater diameter when fitted about the pipe, the edges of the ridges 10 are held against the wall of the hose 12 more tightly, and are more likely to damage the hose.
It is, therefore, an object of this invention to overcome all of the various drawbacks as pointed out above with respect to a hose connecting structure obtained by press fitting a hard pipe into a flexible hose while expanding the latter radially.
According to a first aspect of this invention, there is provided a hose connecting structure comprising a flexible hose having a reinforcing fiber layer in its wall, and a hard pipe a portion of which is press fitted in the hose, wherein the pipe has an annular stop projection formed about its press fitted portion, and having a cross sectional contour including a gentle outward slope from the front end of the projection toward the rear end side to a first corner, which makes the angle of the subsequent second corner gentle, and a rear face at this second corner extending inward toward the longitudinal axis of the pipe at right angles thereto, forming an annular depression.
The structure can be made with high working efficiency using a method in which the hard pipe is press fitted into the flexible hose while the hose is radially expanded. Even if a strong pull-out force may act upon the assembly, the stop projection forming an integral part of the pipe does not come off, or become displaced, but the assembly maintains its pull-out strength and sealing properties.
The structure further has the following advantages:
(1) The stop projection 14 having a gentle slope from the front end toward the rear end side in its cross sectional contour, as shown in FIG. 4A, facilitates the press fitting of the pipe 13 into the hose 15.
(2) The stop projection 14 having in its cross sectional contour a rear face 16 extending from the second corner 17b toward the central longitudinal axis of the pipe 13 at right angles thereto ensures the high pull-out strength and sealing properties of the structure, since the rear face 16 engaging the inner surface of the hose 15 resists strongly any pull-out force acting upon it, as is obvious from FIG. 4B. In this connection, the second corner 17b is not necessarily required to have a sharp angle which is by far smaller than 90xc2x0, but the projection 14 is effective if the second corner 17b has an angle of, say, 70xc2x0 to 110xc2x0.
(3) The second corner 17b of the stop projection 14 has its angle enlarged by the presence of its first corner 17a. It is, therefore, possible to avoid any damaging of the hose by a sharp projection and any resulting lowering of sealing properties as pointed out before in connection with the assembly disclosed in Japanese Patent Application Laid-Open No. 159077/1997.
The hose 15 has a reinforcing fiber layer 18 in its wall. The reinforcing fiber layer 18 does not, however, present any resistance to the press fitting of the pipe 13, since the hose 15 is radially expanded when the pipe 13 is press fitted therein, as is obvious from (1) above. If a pull-out force acts upon the structure, the hose 15 is caused to contract radially, and the reinforcing fiber layer 18 holds the inner surface of the hose 15 strongly against the stop projection 14 to enhance the pull-out strength of the assembly, as is obvious from (2) above. It is, however, possible to avoid any damaging of the hose 15, as is obvious from (3) above.
According to a second aspect of this invention, the hose is radially expanded by at least 20% when the pipe is press fitted thereinto. The radial expansion of the hose to such an extent ensures the still higher pull-out strength and sealing properties of the assembly, while it is still possible to avoid any damaging of the hose by the stop projection on the pipe and any resulting lowering of sealing properties, as explained above.
According to a third aspect of this invention, at least an innermost wall layer of the hose is formed from an elastomer having a tear strength of at least 20 N/mm, such as EPDM (an ethylene-propylene-diene terpolymer) or EPM (an ethylene-propylene copolymer). If the hose is radially expanded by a very high percentage (say, 30 to 50%), there is some possibility or other of the hose being damaged by the stop projection on the pipe, even if its second corner may have an enlarged angle as stated before. The elastomer is effective for protecting the hose under such circumstances.
According to a fourth aspect of this invention, the reinforcing fiber layer has a pull-out strength of at least 0.3 N/mm. The radial expansion of the hose by a very high percentage may cause the separation of the reinforcing fiber layer from the wall of the hose or its displacement and thereby lower the sealing properties of the assembly. However, no such separation or displacement is likely to occur to any hose with a reinforcing layer having a pull-out strength of at least 0.3 N/mm.
The above and other features and advantages of this invention will become more apparent from the following description and the accompanying drawings.